1. Field of the Invention
The disclosed technology relates generally to memory devices, and more particularly to a spin transfer torque (STT) magnetic memory device, a method of manufacturing a spin transfer torque (STT) magnetic memory device and a method of operating a spin transfer torque (STT) magnetic memory device.
2. Description of the Related Technology
Spin transfer torque (STT) magnetic memory devices, sometimes referred to as spin transfer torque random access memory or spin torque transfer random access memory (STT-RAM) devices, refer to a category of nonvolatile memory devices that utilize a change in electrical resistance across a memory cell that can be induced through passage of spin-polarized current. WO2011075257A1, for example, describes a spin transfer torque magnetic memory device comprising a source of spin-polarized electrons and a magnetic material having a magnetization direction representing a state value of a memory bit. Some STT magnetic devices include a source of spin-polarized electrons formed of a magnetization layer, sometimes called a fixed layer, through which spin-unpolarized electrons can pass. The STT magnetic devices also include a magnetic material, sometimes called a free layer having the magnetization direction that can change in response to spin-polarized current, thereby changing the state value of the memory bit. The source of spin-polarized electrons (e.g., the fixed layer) and the magnetic material (e.g.., the free layer) are electrically arranged such that the magnetization direction of the magnetic material can be changed/switched from one direction to another (e.g., flipped) through transfer of spin momentum of the spin-polarized electrons in the magnetization direction. The changing/switching of the magnetization direction can be achieved by passage of sufficient flux of spin-polarized electrons originating from the source (e.g., the fixed layer), which subsequently pass through the magnetic layer (e.g., the free layer). The efficiency of changing/switching of the magnetization direction of the magnetic layer can depend on, among other things, the flux of spin-polarized electrons passing through, for example, the magnetic layer, as described in WO2011075257A1. Under some circumstances, as much as about half of the spin-polarized electrons can be reflected, resulting in a relatively large resistance across the fixed layer. Therefore, there is a need for more efficient STT magnetic memory device.